Such heat exchangers are particularly applicable to motor vehicles where the liquid is the liquid provided to prevent the internal combustion engine from rising to too high a temperature and/or for conditioning the air admitted to the vehicle cabin.
In car construction, where the equipment lightness is of major importance, heat exchangers are commonly made from thin metal tubes of copper, aluminum or aluminum alloy. To enable the thin metal tubes to be simply assembled on a collector or perforated plate, a metal collector plate is generally used, and for many years the ends of the tubes were assembled thereto by soldering.
In more recent techniques which have now become widespread, each of the holes in the collector plate is surrounded by a rim, a sleeve of rubber or the like is interposed between the rim and the end of the tube, and the sleeve is then compressed by expanding the end of the tube, thus sealing the passage of the tube through the collector plate.
Proposals have also been made to use a collector plate of plastic material, mainly in order to facilitate its sealed assembly to a cover which is usually likewise made of plastic material, and which, together with the collector plate constitutes the water box. However, embodiments using plastic material collector plates have not, up to now, given rise to practical applications because of the difficulties in sealing a plastic material collector plate to the metal tubes passing therethrough.
To mitigate the sealing problems which occur with such an assembly, proposals have been made to use a plastic material for the collector plate with substances embedded therein chosen to ensure that the coefficient of thermal expansion of the collector plate is the same as that of the metal tubes passing through it. However, this technique has not solved the wider problem of manufacture which, particularly for motor vehicles, must be simple, cheap, and capable of providing uniform results.
Preferred embodiments of the present invention satisfy these requirements.